Covid carries higher clotting risk than Oxford vaccine
The risk of severe blood clots in the brain from Covid-19 is about eight times greater than the risk associated with taking the Oxford-AstraZeneca vaccine, scientists have found.
The researchers said that the figures, from a database of half a million Covid-19 cases in the US, should help regulators and the public better understand the ‘‘risk-benefit question’’ when looking at the side effects of vaccines.
The study, published before a peer review, found that about 40 in a million people suffered blood clots in the brain two weeks after a coronavirus infection. Of those, about one in five were fatal. Regulators believe that the Oxford-AstraZeneca vaccine is linked to a four to five in a million risk of similar clots.
John Geddes, from Oxford University, said that although this appeared to be a rare side effect of vaccines, it was just one of many caused by the virus.
‘‘A lot of the attention has been taken away and put on the vaccine. The importance of this finding is it brings it back to the fact this is a really horrible illness that has a whole variety of effects.’’
It was not possible to estimate precisely the risk of these kind of clots in the general population, but the scientists said it was likely to be a hundredth the level seen in those who had had Covid19.
The latest data shows that three-quarters of people in England aged over 80 have received two doses of vaccine.
Statistics also confirmed poorer uptake than had been hoped for in care homes. The vaccination rate for staff at older adult care homes is below the level recommended by scientists advising the government in more than half of England’s local authorities.
The vaccination level has risen by only 10 percentage points in two months.
Professor Paul Harrison was in the Oxford team behind the
‘‘The importance of this finding is it brings it back to the fact this is a really horrible illness that has a whole variety of effects.’’ John Geddes Oxford University,
research, none of whom are affiliated with the vaccine group. He said it was when concerns were raised about the blood clots being caused by the vaccine that they looked at similar conditions in Covid-19.
‘‘People haven’t noticed this before because it’s only as the concerns with the vaccine have grown that it becomes important to Covid, even though it is still very very rare in Covid compared with other serious events,’’ he said.
Although Covid is linked to far more common clots, the kind associated with the vaccine are far rarer – rare enough that they were not considered separately as a side effect.
‘‘That’s really why we’ve come to try to turn the debate round and put it back on Covid, because even though [cerebral clotting] is rare it appears to be significantly commoner than in those having the vaccine,’’ he said. ‘‘We think that’s important in helping regulators and the public understand better the risk-benefit question.’’
He added: ‘‘The evidence is that risks of Covid are far greater than risks of the vaccine.’’
Kevin McConway, emeritus professor of applied statistics at the Open University, said that the new study helped, but more data was required.
‘‘A huge amount has been written and said about blood clot risks from vaccines that protect against Covid-19.
‘‘But how rare they are after vaccination, in comparison with how rare they are in unvaccinated people, has been difficult to establish.
‘‘The condition is so rare that really good data on the prevalence in unvaccinated people, before the pandemic, does not really exist.’’